Vitamin D status linked to artery health: study

Increased levels of vitamin D may improve cardiovascular health and
reduce the prevalence of peripheral arterial disease (PAD),
suggests a new study.

Data from 4839 participants of the National Health and Nutrition
Examination Survey (NHANES) showed that the prevalence of PAD was
4.4 per cent lower in people with blood levels of vitamin D above
29.2 nanograms per millilitre (ng/mL) than in people with blood
levels below 17.8 ng/mL.
PAD is associated with decreased blood flow in the legs, and occurs
when arteries in the legs become narrowed or clogged with fatty
deposits. According to 2008 statistic from the American Heart
Association, PAD affects about 8 million Americans and is
associated with significant disease and death.
The authors of the study are careful to point out that the link
does not prove vitamin D is protective in itself (causality), and
recommend increasing intake of the vitamin from fortified foods and
not supplements.
"We would not recommend people start taking vitamin D
supplements without talking to their doctors,"​ stated lead
researcher Michal Melamed, MD, from the Albert Einstein College of
Medicine in New York City. "However, we recommend eating a
balanced diet. People obtain vitamin D either through exposure to
the sun or from foods, especially fish and fortified milk and other
fortified foods."​
The results are published in the journal Arteriosclerosis,
Thrombosis, and Vascular Biology, and were also presented at the
American Heart Association's Arteriosclerosis, Thrombosis and
Vascular Biology Annual Conference 2008.
Study details ​
Blood levels of 25- hydroxyvitamin D (25(OH)D), the non-active
'storage' form of the vitamin, was correlated to the prevalence of
PAD among the participants. The average age of the "large
nationally representative study sample" was 61.2.
When the researcher divided the sample into four groups according
to their 25(OH)D levels, and found that increasing levels of the
vitamin were associated with lower prevalence of PAD, from 8.1 per
cent in the group with the lowest 25(OH)D levels, to 5.4, 4.9, and
3.7 per cent across the 'quartiles' with increasing vitamin D
levels.
When the researchers adjusted for age, sex, race and co-existing
health problems, they found that PAD was 64 per cent more common in
the group with the lowest vitamin D levels compared with the group
with the highest levels. For each 10 ng/mL drop in vitamin D level,
the risk for PAD increased by 29 per cent.
Moreover, the relationship was consistent across the difference
subgroups. "The consistency of the results in these subgroups
is noteworthy,"​ wrote the researchers.
The authors note that the relationship does not prove that
increased levels of vitamin D protect against PAD directly, and
that higher vitamin D levels may be a marker of general or specific
lifestyle practices.
Mechanism ​
The potential mechanism by which vitamin D may improve
cardiovascular health is not known and is "controversial,"​
wrote the authors.
"In some studies, low 25(OH)D levels have been associated with
increased prevalence of coronary heart disease (CHD), stroke, and
congestive heart failure. However, low 25(OH)D has been associated
with a protective association in other studies,"​ they
stated.
Dr. Melamed added: "We know that in mice, vitamin D regulates
one of the hormone systems that affects blood pressure. Since cells
in the blood vessels have receptors for vitamin D, it may directly
affect the vessels, although this has not been fully worked
out." ​
The researchers called for large randomised clinical trials to
address if vitamin D supplementation could offer protection against
PAD.
Vitamin D refers to two biologically inactive precursors - D3, also
known as cholecalciferol, and D2, also known as ergocalciferol. The
former, produced in the skin on exposure to UVB radiation (290 to
320 nm), is said to be more bioactive. The latter is derived from
plants and only enters the body via the diet, from consumption of
foods such as oily fish, egg yolk and liver.
Both D3 and D2 precursors are hydroxylated in the liver and kidneys
to form 25(OH)D, and 1,25-dihydroxyvitamin D (1,25(OH)2D), the
biologically active form that is tightly controlled by the
body.
Source: Arteriosclerosis, Thrombosis, and Vascular
Biology​
Published online ahead of print, April 2008,
doi:10.1161/ATVBAHA.108.165886
"Serum 25-Hydroxyvitamin D Levels and the Prevalence of
Peripheral Arterial Disease. Results from NHANES 2001 to
2004" ​Authors: M.L. Melamed, P. Muntner, E.D. Michos, J.
Uribarri, C. Weber, J. Sharma, P. Raggi